A thin film transistor is mainly formed of a source electrode, a drain electrode, a gate electrode, an active layer and a gate insulating layer. The active layer and the gate insulating layer are two key layers on which performances of a thin film transistor depend. According to different materials of which an active layer is made, thin film transistors may be classified into microcrystalline silicon thin film transistors (c-Si TFTs), amorphous silicon thin film transistors (a-Si TFTs), poly-silicon thin film transistors (p-Si TFTs), organic thin film transistors (OTFTs), and zinc oxide thin film transistors (ZnO TFTs).
P-Si TFTs have advantages such as higher electron mobility, higher aperture ratio, faster response speed and higher resolution, downsizing an assembly greatly and manufacturing integrated drive circuits. As compared with other TFTs, the p-Si TFTs are more suitable for high-frequency display with a large capacity. Moreover, the production cost of the p-Si TFTs is low. Therefore, the p-Si TFTs are used widely.
During the manufacturing of a p-Si TFT, a poly-silicon layer is usually converted from amorphous silicon to poly-silicon through low-pressure chemical vapor deposition, solid phase crystallization, metal induced crystallization, laser annealing treatment or other treatment. However, these processes now have defects such as poor grain uniformity and failure in controlling grain growth direction and grain boundary effectively during the manufacturing. As a result, TFTs with excellent performance cannot be obtained.